Water Power!

You can hear the roar of a waterfall before you spot it. Up close, you may have to crane your neck to see it from top to bottom. Mist sprays your face as water pours over a cliff edge, then crashes into the rocks below.

Joel Scheingross is fascinated by waterfalls. He’s a geologist who studies Earth’s landscapes. Scientists had long thought that waterfalls form when forces, like earthquakes or moving glaciers, create cliffs that rivers flow over.

Scheingross didn’t think those forces could explain some waterfalls he’d seen. He wondered: Can a river flowing over bedrock create its own waterfalls? He designed an investigation to find out.

You can hear the roar of a waterfall before you spot it. You may have to crane your neck once you’re up close. Then you can see it from top to bottom. Water pours over a cliff edge. It crashes into the rocks below. Mist sprays your face.

Joel Scheingross is amazed by waterfalls. He’s a geologist. He studies Earth’s landscapes. Scientists had long thought they knew how waterfalls formed. Earthquakes crack the ground, or moving icy glaciers carve away rock. That creates cliffs. Then rivers flow over them.

Scheingross thought differently. Those forces couldn’t explain some waterfalls he’d seen. He wondered about a river flowing over bedrock. That’s the solid rock under soil. Could one create its own waterfall? He designed an investigation to find out.

Studying waterfalls isn’t easy. They form over thousands of years—too long to observe in a lifetime. Plus, scientists can’t control factors like earthquakes. So Scheingross decided to use a model, or simplified version, of a river for his investigation. 

Engineers built the model inside a three-story warehouse.  Pumps poured water down a 7.3 meter (24 foot) ramp. For bedrock, Scheingross used a material similar to Styrofoam. The foam erodes, or wears away, about 100,000 times faster than real rock. “We could observe thousands of years of erosion in a few hours in the lab,” says Scheingross.

Real rivers carry rocks and sand that grind away bedrock. Scheingross mixed gravel into the water rushing down the ramp. Every 15 minutes, he paused the water to note how the foam bedrock was eroding. He spent the next month starting and stopping the river and recording what changed.

Studying waterfalls isn’t easy. They form over thousands of years. That’s too long to see in a lifetime. Plus, scientists can’t control factors like earthquakes. So Scheingross decided to use a model in his investigation. A model is a simplified river.

Engineers built the model inside a three-story warehouse. Pumps poured water down a 7.3 meter (24 foot) ramp. Scheingross used a material similar to Styrofoam as bedrock. The foam erodes, or wears away. That happens about 100,000 times faster than it does with real rock. “We could observe thousands of years of erosion in a few hours in the lab,” says Scheingross.

Real rivers carry rocks and sand. They grind away bedrock. Scheingross mixed gravel into the water. It rushed down the ramp. He paused the water every 15 minutes. He’d note how the foam bedrock was eroding. He spent the next month starting and stopping the river. Then he’d write down what happened.

In the model waterfall, the landscape transformed quickly. A canyon formed as gravel wore away the foam. Next, pools appeared where waves slammed into the canyon’s walls. If a pool got deep enough, gravel settled on the bottom, protecting the foam. 

Scheingross noticed that sometimes a pool collected gravel while one below it kept eroding. That created a steep cliff. As water poured over the cliff, a waterfall formed. The river had created it—no earthquake needed!

Waterfalls are clues that help geologists understand an area’s history. Scheingross thinks a waterfall in California, called Seven Teacups, formed the way his model showed. Next, he wants to study how often the phenomenon occurs in nature. “This is how science moves forward,” he says.

The landscape changed quickly in the model river. Gravel wore away the foam. A canyon appeared. Waves slammed into the canyon’s walls. They caused pools to form. Some pools became deep. Gravel settled on their bottoms. That protected the remaining foam. 

Scheingross noticed that sometimes a pool collected gravel. But one farther down the river kept eroding. That created a steep cliff. A waterfall formed as water poured over the cliff. The river had created it. There was no earthquake needed!

Waterfalls are clues. They help geologists learn about an area’s history. Scheingross thinks a waterfall in California formed the way his model showed. It’s called Seven Teacups. Next, he wants to study how often the phenomenon occurs in nature. “This is how science moves forward,” he says.